Control circuit for relaxation oscillators



June 22, 1948. R. c. MOORE 2,443,922,

' CONF'ROL CIRCUIT FOR RELAXATION OSCILLATORS v Filed Aug. 2, 1944 CatPatented June 22, 1948 2,443,922 CONTROL cmcorr FOR RELAXATIONOSCILLATORS Robert C. Moore, Philadelphia, Pa., assignor, by mesneassignments, to Philco Corporation, Philadelphia, Pa., a corporation 0!Pennsylvania Application August 2, 1944, Serial No. 547,719 3 Claims.(or 250-36) This invention relates to the control of relaxationoscillators, and more particularly to the control of an oscillator whoseoperation is initiated and maintained in response to a control signal.

It is sometimes desirable to utilize a relaxation oscillator arrangementin which the operation of the oscillator takes place only during theoccurrence of a control signal, i. e., the oscillator is started inresponse to commencement of the control signal and is stopped when thesignal terminates. Prior devices of this character have exhibited anundesirable tendency to produce a transient or disturbance during thestarting of the oscillator,

The principal object of the present invention is to effect improvedcontrol of such an oscillator, and more particularly to effect startingof the oscillator without the production of any undesirable transient ordistur ance.

Another object of the invention is to provide a novel control circuit bywhich the oscillator is started after a predetermined time intervalfollowing the commencement of the control signal, to the end that at theinstant of starting the oscillator shall be conditioned for normaloperation and there shall be no tendency toward the production of anytransient or disturbance.

A further object of the invention is to provide a novel control circuitof the stated character in conjunction with a relaxation oscillator ofthe multivibrator type.

Other objects and advantages of the invention will become apparentduring the course of the following description with reference to theaccompanying drawings, in which:

Fig. 1 illustrates schematically one embodiment of the invention; and

Fig. 2 is an explanatory diagram illustrating the voltage wave forms atvarious parts of the circuit of Fig. 1.

Referring to Fig. 1, there is shown a relaxation oscillator of themultivibrator type comprising vacuum tubes T2 and T3 and theirassociated circuit elements. A control tube T1 and its associatedcircuit elements serve to control the operation of the multivibrator.While the tubes are shown as triodes, it is to be understood thatmulti-grid tubes maybe employed together with the necessary circuitmodifications to accommodate the particular tubes employed in anyinstance. Furthermore, tubes T2 and T3 may be combined in one envelope,as in the well known twin type vacuum tube.

The control tube T1 is arranged to receive a negative timing pulsethrough a grid coupling condenser ll). Preferably the grid of tube T1 isoperated at zero bias, being connected to the cathode by means of gridresistor H. The cathode of tube T1 is connected to ground through avariable cathode resistor or potentiometer l2, shunted by a condenseriii. The anode of tube T1 is directly connected to the grid of the firstmultivibrator tube T2 and may receive its potential from the cathodecircuit of the multivibrator by way of grid resistor l4. Alternatively,the return for grid resistor I4 (and also resistor l9) may be made to aseparate supply. The two tubes T2 and T3 are arranged generally inconventional multivibrator fashion, with the cathodes tied together andconnected to ground through a common cathode biasing resistor 15 havinga by-pass condenser It. The grid coupling condenser and plate loadresistor :t'or tube T2 are shown at I! and 18, respectively, while thegrid resistor. grid condenser and plate resistor for tube T2 arerepresented at 19, 20 and 2|. A suitable source IB+ serves as the anodepotential supply for the multivibrator tubes T2 and T3. A resistancenetwork consisting of resistor 22 and potentiometer 23, in series, maybe connected between the anode voltage supply B+ and the common cathodeconnection of tubes T2 and T2. By connecting the grid resistors l4 andIQ of tubes T2 and T2 to the movable arm 24 of potentiometer 23, anarrangement is provided for controlling and adjusting the frequency ofthe multivibrator.

The input terminal of the device is shown at 25, while the output of themultivibrator may be obtained from the anode of tlibe T3 by way of theoutput terminal 26.

It will be apparent to those familiar with the art that grid resistor llof control tube T1 may, alternatively, be connected to ground instead ofto the cathode of tube T1, as shown in Fig. l, in which casepotentiometer l2 would become a variable cathode biasing resistor.

The operation of the circuit will now be de-' scribed with reference tothe embodiment shown in Fig. 1 and the voltage wave forms of Fig. 2.

With no signal applied to the grid of control tube Tl, this tube isconducting since its grid is at zero bias, and the magnitude of itsplate current is governed in part by the adjustment of potentiometer I2.The plate current of tube T1. flowing through grid resistor l4, produces9. voltage drop thereacross which biases the grid of tube T2 well belowcut-off, thereby preventing tube T2 from conducting and preventing themultivibrator from oscillating. The other multi- 3 vibrator tube '1':is, of course, conducting since its grid is at cathode potential or.some small positive potentiahdepending upon the positio ofpotentiometer arm 24. r

fThe voltage wave forms at several parts of the circuit for thisno-signal input condition are shown in Fig. 2 for the interval betweenthe time reference lines t1t2. Referring toFig. 2, the grid potential oftube T1 with respect to its cathode islrepresented by curve egTl; thepotential of the grid of tube T: with respect to its cathode isrepresented by curve e Tz, the dotted lines indieating other potentialsfor diiferent settings of the potentiometer I2; the potential on theplate of tube T2, which is approximately equal to the supply voltage B+since this tube is not conducting, is represented by curve ,e Ta; thegrid potential of tube T3 with respect to its cathode, assuming that thecontact arm 24 or potentiometer 23 in Fig. 1 is at the cathode end, iszero as represented at 831 3; and the potential on the plate of tube T:which is conducting, iszrepresented by curve epT3.

Referring again to Fig. 1, when a negative pulse is applied to the inputterminal 25, driving the grid potential of tube Tl below its cut-oilvalue, the grid potential of tube T2 rises as the charge on gridcondenser ll leaks oil through resistor l4 and the conducting tube T3.When the grid potential of tube T2 reaches its cut-ofi value, this tubeconducts and the multivibrator begins to oscillate in normalmultivibrator fashion. The multivibrator will then continue to functionfor the duration of the negative pulse on the grid of control tube Ti.At the end of this timing pulse, the grid potential of tube Tl rises toits normal no signal value, whereupon tube Tl conducts, thereby loweringthe grid potential of tube T2 below its cut-oii value and interruptingmulti vibrator oscillation. The application of another negative timingpulse causes repetition of the above cycle of operation.

The voltage conditions in "the circuit during the .interval between thecommencement of the negative timing pulseand the time that the gridpotential of tube T2 reaches its cut-oil value are represented in Fig. 2between the vertical lines 12-42. It will be noted that the only changesin the circuit conditions are the drop in grid po- .tential of tube T1to so: .e value below'cut-ofl, as shown by curve egTl, and theexponential rise in grid voltage of tube T2, as shown by curve 8gT2. Atthe instant the grid potential of tube T2 reaches its cut-oil value, i.e., at time is, the multivibrator is ready to function in its normalmanner, as indicated by the grid voltage and plate vpltage wave formsfor tubes T2 and T3 in Fig. 2, since the voltages on the plate of tubeTa and on the grid and plate of tube T2 are identical to thoseconditions during that portion of the multivibrator cycle when the gridvoltage of tube Ta is below its cut-ofi valu Since themultivibrator goesinto oscillation at some time, t3 in Fig. 2, after theapplication of thenegative pulse at time t2, it is apparent from wave form egT2 that thetime ta, at which multivibrator action begins, depends upon thepotential of the grid of tube T2 during the no signal input period. Thedotted lines in Fig. 2 for the grid potential of tube T2 (wave form eTz) show that for less negative potentials the time required for thegrid of tube T2 to reach its cut-off value is shorter than for morenegative potentials. The delay interval between the time of applicationof the negative timing pulse to the input ter- Condensers lll-0.005microfarad Resistor I I220,000 ohms.

Potentiometer |2-l00,000 ohms.

Condensers l3 and I 6-0.005 microfarad each Resistors It and Iii-100,000ohms each Resistor Iii-4,700 ohms Condensers l1 and 20l00micrmmicrofarads each Resistors l8 and ii-4,700 ohms each,

Resistor 22--l50,000 ohms Potentiometer 23-25,000 ohms It will beunderstood, of course, that the invention is not limited to the specificembodiment illustrated and described herein nor to the values of thevarious elements given as a specific example. The invention is capableof various embodiments or modifications which may be resorted to withoutdeparting from its scope.

I claim:

1. In combination, a multivibrator comprising a pair of inter-coupledvacuum tubes having at least triode elements, means normally biasing thegrid of one of said tubes below cut-oil value, thereby rendering saidmultivibrator normally inoperative, means responsive to a control signalfor decreasingthe bias of said one grid so as to render saidmultivibrator operative .for the duration of said signal only, and meansfor delaying the starting of said multivibrator for a predetermined timeinterval following the commencement of said signal.

2. In combination, a multivibrator comprising a pair of inter-coupledvacuum tubes having at least triode elements, a normally conductivecontrol tube, means controlled by the anode current of said control tubefor normally biasing the id of one of said multivibrator tubes belowcut-oii value, thereby rendering said multivibrator normallyinoperative, means for applying to said control tube a control signaladapted to reduce the anode current of the control tube and therebydecrease the bias of said grid, so as to render said multivibratoroperative for the duration of said signal only, and means for delayingthestarting of said multivibrator for a predetermined time intervalfollowing the commencement of said signal.

3. In combination, a multivibrator comprising a pair of inter-coupledvacuum tubes having at least triode elements, a resistor connectedbetween the grid and cathode of one of said tubes. a control, tubehaving its anode connected to the junction between said resistor andsaid grid, 8. source of anode potential connected to the opposite end ofsaid resistor, whereby said resistor serves to bias said grid undercontrol of the anode current of said control tube, means for normallyoperating said control tube so as to bias said grid below cut-off Valuethereby rendering said multivibrator normally inoperative, means forapplying to said control tube a control signal adapted to reduce theanode current of the control tube REFERENCES CITED The followingreferences are of record in the file of this patent:

7 Number UNITEDSTATES PATENTS Name Date Lubke Apr. 14, 1936 Smith Oct.11, 1938 Reeves Dec. 16, 1941 Geiger May 5, 1942 Bartelink Dec. 19, 1944Morrison Aug. 20, 1946

